“Hosts and parasites are often studied as pair-wise interactions, without considering the ecological communities within which they interact,” wrote Hunter in his project summary. “This is problematic because other species in food webs may significantly alter parasite virulence and transmission, two traits that drive the evolutionary and ecological dynamics of host-parasite interactions.”

Hunter’s research will address this knowledge gap by examining how belowground species interactions alter the virulence and transmission of a host-specific parasite above ground. “In particular, the project will focus upon an interaction between monarch butterflies and their protozoan parasites, the milkweeds that monarchs use as larval food plants, and the mycorrhizal fungi that interact with milkweed roots.”

Such community-mediated indirect effects should be pervasive. For example, diverse organisms use natural products from their community members as medicines. In terrestrial plants, the expression of medicinal natural products is influenced strongly by mycorrhizal fungi.

The research project has two specific aims. “First, experiments will determine how different species and densities of mycorrhizal fungi affect the foliar composition of cardenolides (secondary milkweed chemicals that are toxic to monarch butterfly parasites) and the subsequent virulence and transmission potential of monarch parasites. Second, experiments will examine how mycorrhizal fungi affect the medication behavior of monarch butterflies. Previous work has shown that infected monarchs increase their offspring’s fitness by preferentially laying their eggs on high-cardenolide milkweed. The research will extend this work by determining whether mycorrhizal fungi alter the medicinal properties of milkweeds and thereby the oviposition preferences of infected monarchs.

Hunter’s research will integrate research with education in several ways. Many experiments are suitable as stand-alone projects, and students of multiple levels (undergraduate and graduate) and from diverse backgrounds will participate in the design, execution and presentation of this work. Dr. Jaap de Roode at Emory University, a collaborator in the research, also received funding from NSF.